dracut-functions.sh: Fix check_block_and_slaves_all

dracut-functions.sh: Fix check_block_and_slaves_all

check_block_and_slaves_all $func $dev should return 0, if $func return 0
for any checked device. Currently if any device don't have any sub
device, 1 is returned instead.

So remove the sub device checking statement. Also remove the same
statement in check_block_and_slaves, the "[[ -f $_x/dev ]]" in the for
loop is enought to ensure sub device exists.

Signed-off-by: Kairui Song <kasong@redhat.com>